+/* Analyze differences between two vectors.
+
+ Copyright (C) 1988-1989, 1992-1995, 2001-2004, 2006-2013 Free Software
+ Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+
+/* The basic idea is to consider two vectors as similar if, when
+ transforming the first vector into the second vector through a
+ sequence of edits (inserts and deletes of one element each),
+ this sequence is short - or equivalently, if the ordered list
+ of elements that are untouched by these edits is long. For a
+ good introduction to the subject, read about the "Levenshtein
+ distance" in Wikipedia.
+
+ The basic algorithm is described in:
+ "An O(ND) Difference Algorithm and its Variations", Eugene Myers,
+ Algorithmica Vol. 1 No. 2, 1986, pp. 251-266;
+ see especially section 4.2, which describes the variation used below.
+
+ The basic algorithm was independently discovered as described in:
+ "Algorithms for Approximate String Matching", E. Ukkonen,
+ Information and Control Vol. 64, 1985, pp. 100-118.
+
+ Unless the 'find_minimal' flag is set, this code uses the TOO_EXPENSIVE
+ heuristic, by Paul Eggert, to limit the cost to O(N**1.5 log N)
+ at the price of producing suboptimal output for large inputs with
+ many differences. */
+
+/* Before including this file, you need to define:
+ ELEMENT The element type of the vectors being compared.
+ EQUAL A two-argument macro that tests two elements for
+ equality.
+ OFFSET A signed integer type sufficient to hold the
+ difference between two indices. Usually
+ something like ssize_t.
+ EXTRA_CONTEXT_FIELDS Declarations of fields for 'struct context'.
+ NOTE_DELETE(ctxt, xoff) Record the removal of the object xvec[xoff].
+ NOTE_INSERT(ctxt, yoff) Record the insertion of the object yvec[yoff].
+ EARLY_ABORT(ctxt) (Optional) A boolean expression that triggers an
+ early abort of the computation.
+ USE_HEURISTIC (Optional) Define if you want to support the
+ heuristic for large vectors.
+ It is also possible to use this file with abstract arrays. In this case,
+ xvec and yvec are not represented in memory. They only exist conceptually.
+ In this case, the list of defines above is amended as follows:
+ ELEMENT Undefined.
+ EQUAL Undefined.
+ XVECREF_YVECREF_EQUAL(ctxt, xoff, yoff)
+ A three-argument macro: References xvec[xoff] and
+ yvec[yoff] and tests these elements for equality.
+ Before including this file, you also need to include:
+ #include <limits.h>
+ #include <stdbool.h>
+ #include "minmax.h"
+ */
+
+/* Maximum value of type OFFSET. */
+#define OFFSET_MAX \
+ ((((OFFSET)1 << (sizeof (OFFSET) * CHAR_BIT - 2)) - 1) * 2 + 1)
+
+/* Default to no early abort. */
+#ifndef EARLY_ABORT
+# define EARLY_ABORT(ctxt) false
+#endif
+
+/* Use this to suppress gcc's "...may be used before initialized" warnings.
+ Beware: The Code argument must not contain commas. */
+#ifndef IF_LINT
+# ifdef lint
+# define IF_LINT(Code) Code
+# else
+# define IF_LINT(Code) /* empty */
+# endif
+#endif
+
+/* As above, but when Code must contain one comma. */
+#ifndef IF_LINT2
+# ifdef lint
+# define IF_LINT2(Code1, Code2) Code1, Code2
+# else
+# define IF_LINT2(Code1, Code2) /* empty */
+# endif
+#endif
+
+/*
+ * Context of comparison operation.
+ */
+struct context
+{
+ #ifdef ELEMENT
+ /* Vectors being compared. */
+ ELEMENT const *xvec;
+ ELEMENT const *yvec;
+ #endif
+
+ /* Extra fields. */
+ EXTRA_CONTEXT_FIELDS
+
+ /* Vector, indexed by diagonal, containing 1 + the X coordinate of the point
+ furthest along the given diagonal in the forward search of the edit
+ matrix. */
+ OFFSET *fdiag;
+
+ /* Vector, indexed by diagonal, containing the X coordinate of the point
+ furthest along the given diagonal in the backward search of the edit
+ matrix. */
+ OFFSET *bdiag;
+
+ #ifdef USE_HEURISTIC
+ /* This corresponds to the diff -H flag. With this heuristic, for
+ vectors with a constant small density of changes, the algorithm is
+ linear in the vectors size. */
+ bool heuristic;
+ #endif
+
+ /* Edit scripts longer than this are too expensive to compute. */
+ OFFSET too_expensive;
+
+ /* Snakes bigger than this are considered "big". */
+ #define SNAKE_LIMIT 20
+};
+
+struct partition
+{
+ /* Midpoints of this partition. */
+ OFFSET xmid;
+ OFFSET ymid;
+
+ /* True if low half will be analyzed minimally. */
+ bool lo_minimal;
+
+ /* Likewise for high half. */
+ bool hi_minimal;
+};
+
+
+/* Find the midpoint of the shortest edit script for a specified portion
+ of the two vectors.
+
+ Scan from the beginnings of the vectors, and simultaneously from the ends,
+ doing a breadth-first search through the space of edit-sequence.
+ When the two searches meet, we have found the midpoint of the shortest
+ edit sequence.
+
+ If FIND_MINIMAL is true, find the minimal edit script regardless of
+ expense. Otherwise, if the search is too expensive, use heuristics to
+ stop the search and report a suboptimal answer.
+
+ Set PART->(xmid,ymid) to the midpoint (XMID,YMID). The diagonal number
+ XMID - YMID equals the number of inserted elements minus the number
+ of deleted elements (counting only elements before the midpoint).
+
+ Set PART->lo_minimal to true iff the minimal edit script for the
+ left half of the partition is known; similarly for PART->hi_minimal.
+
+ This function assumes that the first elements of the specified portions
+ of the two vectors do not match, and likewise that the last elements do not
+ match. The caller must trim matching elements from the beginning and end
+ of the portions it is going to specify.
+
+ If we return the "wrong" partitions, the worst this can do is cause
+ suboptimal diff output. It cannot cause incorrect diff output. */
+
+static void
+diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal,
+ struct partition *part, struct context *ctxt)
+{
+ OFFSET *const fd = ctxt->fdiag; /* Give the compiler a chance. */
+ OFFSET *const bd = ctxt->bdiag; /* Additional help for the compiler. */
+#ifdef ELEMENT
+ ELEMENT const *const xv = ctxt->xvec; /* Still more help for the compiler. */
+ ELEMENT const *const yv = ctxt->yvec; /* And more and more . . . */
+ #define XREF_YREF_EQUAL(x,y) EQUAL (xv[x], yv[y])
+#else
+ #define XREF_YREF_EQUAL(x,y) XVECREF_YVECREF_EQUAL (ctxt, x, y)
+#endif
+ const OFFSET dmin = xoff - ylim; /* Minimum valid diagonal. */
+ const OFFSET dmax = xlim - yoff; /* Maximum valid diagonal. */
+ const OFFSET fmid = xoff - yoff; /* Center diagonal of top-down search. */
+ const OFFSET bmid = xlim - ylim; /* Center diagonal of bottom-up search. */
+ OFFSET fmin = fmid;
+ OFFSET fmax = fmid; /* Limits of top-down search. */
+ OFFSET bmin = bmid;
+ OFFSET bmax = bmid; /* Limits of bottom-up search. */
+ OFFSET c; /* Cost. */
+ bool odd = (fmid - bmid) & 1; /* True if southeast corner is on an odd
+ diagonal with respect to the northwest. */
+
+ fd[fmid] = xoff;
+ bd[bmid] = xlim;
+
+ for (c = 1;; ++c)
+ {
+ OFFSET d; /* Active diagonal. */
+ bool big_snake = false;
+
+ /* Extend the top-down search by an edit step in each diagonal. */
+ if (fmin > dmin)
+ fd[--fmin - 1] = -1;
+ else
+ ++fmin;
+ if (fmax < dmax)
+ fd[++fmax + 1] = -1;
+ else
+ --fmax;
+ for (d = fmax; d >= fmin; d -= 2)
+ {
+ OFFSET x;
+ OFFSET y;
+ OFFSET tlo = fd[d - 1];
+ OFFSET thi = fd[d + 1];
+ OFFSET x0 = tlo < thi ? thi : tlo + 1;
+
+ for (x = x0, y = x0 - d;
+ x < xlim && y < ylim && XREF_YREF_EQUAL (x, y);
+ x++, y++)
+ continue;
+ if (x - x0 > SNAKE_LIMIT)
+ big_snake = true;
+ fd[d] = x;
+ if (odd && bmin <= d && d <= bmax && bd[d] <= x)
+ {
+ part->xmid = x;
+ part->ymid = y;
+ part->lo_minimal = part->hi_minimal = true;
+ return;
+ }
+ }
+
+ /* Similarly extend the bottom-up search. */
+ if (bmin > dmin)
+ bd[--bmin - 1] = OFFSET_MAX;
+ else
+ ++bmin;
+ if (bmax < dmax)
+ bd[++bmax + 1] = OFFSET_MAX;
+ else
+ --bmax;
+ for (d = bmax; d >= bmin; d -= 2)
+ {
+ OFFSET x;
+ OFFSET y;
+ OFFSET tlo = bd[d - 1];
+ OFFSET thi = bd[d + 1];
+ OFFSET x0 = tlo < thi ? tlo : thi - 1;
+
+ for (x = x0, y = x0 - d;
+ xoff < x && yoff < y && XREF_YREF_EQUAL (x - 1, y - 1);
+ x--, y--)
+ continue;
+ if (x0 - x > SNAKE_LIMIT)
+ big_snake = true;
+ bd[d] = x;
+ if (!odd && fmin <= d && d <= fmax && x <= fd[d])
+ {
+ part->xmid = x;
+ part->ymid = y;
+ part->lo_minimal = part->hi_minimal = true;
+ return;
+ }
+ }
+
+ if (find_minimal)
+ continue;
+
+#ifdef USE_HEURISTIC
+ /* Heuristic: check occasionally for a diagonal that has made lots
+ of progress compared with the edit distance. If we have any
+ such, find the one that has made the most progress and return it
+ as if it had succeeded.
+
+ With this heuristic, for vectors with a constant small density
+ of changes, the algorithm is linear in the vector size. */
+
+ if (200 < c && big_snake && ctxt->heuristic)
+ {
+ {
+ OFFSET best = 0;
+
+ for (d = fmax; d >= fmin; d -= 2)
+ {
+ OFFSET dd = d - fmid;
+ OFFSET x = fd[d];
+ OFFSET y = x - d;
+ OFFSET v = (x - xoff) * 2 - dd;
+
+ if (v > 12 * (c + (dd < 0 ? -dd : dd)))
+ {
+ if (v > best
+ && xoff + SNAKE_LIMIT <= x && x < xlim
+ && yoff + SNAKE_LIMIT <= y && y < ylim)
+ {
+ /* We have a good enough best diagonal; now insist
+ that it end with a significant snake. */
+ int k;
+
+ for (k = 1; XREF_YREF_EQUAL (x - k, y - k); k++)
+ if (k == SNAKE_LIMIT)
+ {
+ best = v;
+ part->xmid = x;
+ part->ymid = y;
+ break;
+ }
+ }
+ }
+ }
+ if (best > 0)
+ {
+ part->lo_minimal = true;
+ part->hi_minimal = false;
+ return;
+ }
+ }
+
+ {
+ OFFSET best = 0;
+
+ for (d = bmax; d >= bmin; d -= 2)
+ {
+ OFFSET dd = d - bmid;
+ OFFSET x = bd[d];
+ OFFSET y = x - d;
+ OFFSET v = (xlim - x) * 2 + dd;
+
+ if (v > 12 * (c + (dd < 0 ? -dd : dd)))
+ {
+ if (v > best
+ && xoff < x && x <= xlim - SNAKE_LIMIT
+ && yoff < y && y <= ylim - SNAKE_LIMIT)
+ {
+ /* We have a good enough best diagonal; now insist
+ that it end with a significant snake. */
+ int k;
+
+ for (k = 0; XREF_YREF_EQUAL (x + k, y + k); k++)
+ if (k == SNAKE_LIMIT - 1)
+ {
+ best = v;
+ part->xmid = x;
+ part->ymid = y;
+ break;
+ }
+ }
+ }
+ }
+ if (best > 0)
+ {
+ part->lo_minimal = false;
+ part->hi_minimal = true;
+ return;
+ }
+ }
+ }
+#endif /* USE_HEURISTIC */
+
+ /* Heuristic: if we've gone well beyond the call of duty, give up
+ and report halfway between our best results so far. */
+ if (c >= ctxt->too_expensive)
+ {
+ OFFSET fxybest;
+ OFFSET fxbest IF_LINT (= 0);
+ OFFSET bxybest;
+ OFFSET bxbest IF_LINT (= 0);
+
+ /* Find forward diagonal that maximizes X + Y. */
+ fxybest = -1;
+ for (d = fmax; d >= fmin; d -= 2)
+ {
+ OFFSET x = MIN (fd[d], xlim);
+ OFFSET y = x - d;
+ if (ylim < y)
+ {
+ x = ylim + d;
+ y = ylim;
+ }
+ if (fxybest < x + y)
+ {
+ fxybest = x + y;
+ fxbest = x;
+ }
+ }
+
+ /* Find backward diagonal that minimizes X + Y. */
+ bxybest = OFFSET_MAX;
+ for (d = bmax; d >= bmin; d -= 2)
+ {
+ OFFSET x = MAX (xoff, bd[d]);
+ OFFSET y = x - d;
+ if (y < yoff)
+ {
+ x = yoff + d;
+ y = yoff;
+ }
+ if (x + y < bxybest)
+ {
+ bxybest = x + y;
+ bxbest = x;
+ }
+ }
+
+ /* Use the better of the two diagonals. */
+ if ((xlim + ylim) - bxybest < fxybest - (xoff + yoff))
+ {
+ part->xmid = fxbest;
+ part->ymid = fxybest - fxbest;
+ part->lo_minimal = true;
+ part->hi_minimal = false;
+ }
+ else
+ {
+ part->xmid = bxbest;
+ part->ymid = bxybest - bxbest;
+ part->lo_minimal = false;
+ part->hi_minimal = true;
+ }
+ return;
+ }
+ }
+ #undef XREF_YREF_EQUAL
+}
+
+
+/* Compare in detail contiguous subsequences of the two vectors
+ which are known, as a whole, to match each other.
+
+ The subsequence of vector 0 is [XOFF, XLIM) and likewise for vector 1.
+
+ Note that XLIM, YLIM are exclusive bounds. All indices into the vectors
+ are origin-0.
+
+ If FIND_MINIMAL, find a minimal difference no matter how
+ expensive it is.
+
+ The results are recorded by invoking NOTE_DELETE and NOTE_INSERT.
+
+ Return false if terminated normally, or true if terminated through early
+ abort. */
+
+static bool
+compareseq (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim,
+ bool find_minimal, struct context *ctxt)
+{
+#ifdef ELEMENT
+ ELEMENT const *xv = ctxt->xvec; /* Help the compiler. */
+ ELEMENT const *yv = ctxt->yvec;
+ #define XREF_YREF_EQUAL(x,y) EQUAL (xv[x], yv[y])
+#else
+ #define XREF_YREF_EQUAL(x,y) XVECREF_YVECREF_EQUAL (ctxt, x, y)
+#endif
+
+ /* Slide down the bottom initial diagonal. */
+ while (xoff < xlim && yoff < ylim && XREF_YREF_EQUAL (xoff, yoff))
+ {
+ xoff++;
+ yoff++;
+ }
+
+ /* Slide up the top initial diagonal. */
+ while (xoff < xlim && yoff < ylim && XREF_YREF_EQUAL (xlim - 1, ylim - 1))
+ {
+ xlim--;
+ ylim--;
+ }
+
+ /* Handle simple cases. */
+ if (xoff == xlim)
+ while (yoff < ylim)
+ {
+ NOTE_INSERT (ctxt, yoff);
+ if (EARLY_ABORT (ctxt))
+ return true;
+ yoff++;
+ }
+ else if (yoff == ylim)
+ while (xoff < xlim)
+ {
+ NOTE_DELETE (ctxt, xoff);
+ if (EARLY_ABORT (ctxt))
+ return true;
+ xoff++;
+ }
+ else
+ {
+ struct partition part IF_LINT2 (= { .xmid = 0, .ymid = 0 });
+
+ /* Find a point of correspondence in the middle of the vectors. */
+ diag (xoff, xlim, yoff, ylim, find_minimal, &part, ctxt);
+
+ /* Use the partitions to split this problem into subproblems. */
+ if (compareseq (xoff, part.xmid, yoff, part.ymid, part.lo_minimal, ctxt))
+ return true;
+ if (compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal, ctxt))
+ return true;
+ }
+
+ return false;
+ #undef XREF_YREF_EQUAL
+}
+
+#undef ELEMENT
+#undef EQUAL
+#undef OFFSET
+#undef EXTRA_CONTEXT_FIELDS
+#undef NOTE_DELETE
+#undef NOTE_INSERT
+#undef EARLY_ABORT
+#undef USE_HEURISTIC
+#undef XVECREF_YVECREF_EQUAL
+#undef OFFSET_MAX
projects / gnulib.git / blobdiff